BOPET films with a low coat weight matte coating, antimicrobial properties, and excellent paint and ink adhesion properties are desirable for multiple applications such as food packaging, decorative, label and solar window film to name a few.
The food packaging industry commonly uses BOPET in many heat sealable applications to take advantage of the intrinsic properties of BOPET such as clarity and tensile strength. Typically, a heat sealable layer is a layer of a polymer that will melt at an elevated above room temperature, e.g., between 375° F.-425° F., thereby forming a bond with another substrate when pressed together with heat and pressure.
BOPET can be coextruded to yield 2 distinct layers, an APET (amorphous polyester) layer, which is suitable for heat sealing because of its lower Tg or can be used as an adhesion promoting surface, and a CPET (crystallized polyester) layer. Typically, an amorphous polyester layer contains distribution of polymer chains that are completely random allowing the onset of molecular motion to take place at lower temperatures than the crystallization temperature of the polyester) Also, physical stretching (orientation) of polyester at a temperature below the melting point can create a three dimensional ordered phase. This ordered phase can result in crystallinity and determine the crystalline properties of the polymer such as density, optical clarity, modulus and mechanical response.
Typically, a matte finish coating is applied after the machine direction orientation (MDO) and the wet coating is dried simultaneously as the film is being oriented in the transverse direction. (TDO). U.S. Pat. No. 5,906,823 discloses Triclosan as an antimicrobial additive in PVC films for gloves. Triclosan (IUPAC name: 5-chloro-2-(2,4-dichlorophenoxy)phenol) is an antibacterial and antifungal agent found in consumer products, including soaps, detergents, toys, and surgical cleaning treatments.
U.S. Pat. No. 6,884,741 discloses a water based antimicrobial in a porous sheeting substrate. U.S. Pat. No. 7,960,010 discloses silver zeolite particles as an antimicrobial additive in an extruded layer. U.S. Pat. No. 8,613,829 discloses the addition of antimicrobials to paper substrates. U.S. Pat. No. 8,900,696 discloses ammonium silanes as antimicrobial additives in a coating on PET but does not disclose that transverse orientation during matte coating can increase matteing efficiency or particle distribution.
Pigment particles are generally added to reduce the gloss of coatings and primers. The increase in particle size generally decreases the gloss of surface coatings.
Typically, high aspect ratio pigments such as clay, vermiculite are aligned parallel to the surface after drying while small sized pigments are lost below the surface of the dried polymer of the coating and do not affect the surface roughness. On rough surfaces the light is diffusely scattered in all directions. The image forming qualities are diminished: A reflected object no longer appears brilliant, but blurred. The more uniform the light is scattered, the less intense the reflection in the main direction and the surface will appear duller. A number of standard parameters are used to describe surface roughness. In the background and embodiments herein, roughness means Rq or root mean square roughness (RRMS), i.e., the square root of the sum of the squares of the individual heights and depths from the mean line, defined as:
      R    q    =                    1        n            ⁢                        ∑                      i            =            1                    n                ⁢                  y          i          2                    
The roughness profile contains n ordered, equally spaced points along the trace, and yi is the vertical distance from the mean line to the ith data point. Height is assumed to be positive in the up direction, away from the bulk material.
Decreasing gloss depends mostly on the surface topography or heights and depths of the surface. In general, coatings with smooth surfaces (where the angle of incidence is equal to the angle of reflection) have high gloss (greater than 70 GU as measured by a byk glossmeter). Rough surfaces diffuse light so they appear dull or not as bright as a smooth surface. As roughness gets higher, light scattering increases which causes gloss to decrease.
Gloss is a measure of reflectivity of light from a coated surface. The angle at which a surface is viewed gives different gloss measurements. Gloss can be measured by devices like the BYK gloss meters made by BYK-Gardner USA, which also give readings at different angles.
Another factor effecting gloss is the dynamics of film shrinkage that occurs during drying of the coating on the film. The resin system that make up the film, the solids content, the amount and type of solvents and the drying method all play a role in film shrinkage, which in turn affects the gloss of the surface. Generally, each resin system exhibits a unique curing phenomenon during drying.
Shrinkage of the coating on the coated film can produce a matte finish of the coating. After applying the coating, the solvent/water starts to evaporate, the viscosity increases, and the coating solidifies, until the final drying when the coating becomes hard and elastic. The evaporation of solvents causes the matting pigments to be distributed throughout the whole coated film, making the coating thickness of the coating to become thinner. This decrease in thickness can produce a micro rough surface. Typically, coatings with high volatile organic compounds are easier to matte than coatings with high solid content. Therefore, UV coatings with nearly 100% or 100% solid content tend to be difficult to matte.